1. Field of the Invention
The subject matter of this invention relates generally to processes for making oil submersible fuses and it relates more particularly to making fuses with epoxy resin seals which maintain their sealing integrity over a wide temperature range.
2. Description of the Prior Art
It is known in the prior art to make cartridge-type fuses having annular grooves at the ends thereof in which overlaid or telescoped conductive ferrules may be magneformed or crimped for enclosing the ends of the fuse securely. Such a fuse is taught in U.S. Pat. No. 3,855,563 issued Dec. 17, 1974 to F. L. Cameron et al and in U.S. Pat. No. 3,333,336 issued Aug. 1, 1967 to F. L. Cameron et al. Both of the above patents are assigned to the assignee of the present invention. An electromagnetic crimping or securing process is taught in the latter noted U.S. Patent. It is also known to generally provide some form of seal at the interface between the edge of a fuse ferrule and the protective fuse barrel or body to generally prevent the surrounding environment from affecting the internal portion of the fuse. Such a fuse is taught in U.S. Pat. No. 3,911,385 issued Oct. 7, 1975 to D. D. Blewitt et al. In that case a sealant such as silicone rubber is disposed as a bead between the edge of a ferrule and an epoxy-covered glass melamine fuse ferrule. The fuse described in that case is for outdoor use where the fuse is likely to be exposed to a relatively hostile environment. The bead is provided to enhance the weatherproof qualities of the fuse. None of the prior art apparently teaches the use of a seal between a fuse ferrule and protective body for a fuse which is submersible in hot oil such as might be found in a transformer which may be part of an underground electrical distribution system. The relatively high current ratings and high operating temperatures for the oil of such a system exceeded known fuse sealing material's capability particularly as regards to resistance to hot transformer oil. Furthermore, it has been found that attempting to apply epoxy resin to a fuse barrel for sealing it is difficult to center the ferrule relative to the tube to allow the epoxy resin to flow evenly around all parts of the interface between the ferrule and the tube. This problem produces an epoxy deficient dry seal area. It has also been found that after applying liquid epoxy resin at room temperature the subsequent curing process, i.e., the raising of the temperature of the tube subsequent to apporoximately 140.degree. C., causes trapped gas (air) to expand through the still liquid or gelatinous epoxy causing blowout paths or vent holes therein. These paths or holes form potential leak regions when the fuse is submersed in oil. It would be advantageous therefore if a seal for an oil submersible fuse could be found which would operate in a relatively hot transformer oil environment and which had sufficient flexibility and adhesion properties to maintain an oil-resistant sealing capability over a wide range of temperature.